"""
题目：编写一个函数，输入n为偶数时，调用函数求1/2+1/4+...+1/n,当输入n为奇数时，调用函数1/1+1/3+...+1/n(利用指针函数)
"""
from Tools.scripts.treesync import raw_input


def peven(n):
	i = 0
	s = 0.0
	for i in range(2, n + 1, 2):
		s += 1.0 / i
	return s


def podd(n):
	s = 0.0
	for i in range(1, n + 1, 2):
		s += 1 / i
	return s


def dcall(fp, n):
	s = fp(n)
	return s


if __name__ == '__main__':
	n = int(raw_input('input a number:\n'))
	if n % 2 == 0:
		sum = dcall(peven, n)
	else:
		sum = dcall(podd, n)
	print(sum)
